A cyclopentene ring-opening polymer obtained by metathesis ring-opening polymerization of cyclopentene is widely known as a rubber material. It is used as various types of rubber materials by mixing in for example a filler such as carbon black or silica. In general, a cyclopentene ring-opening polymer, as for example disclosed in Patent Document 1, is produced by bulk polymerization or solution polymerization using a so-called Ziegler-Natta catalyst comprised of a transition metal compound of Group VI of the Periodic Table such as WCl6 or MoCl5 and an organometallic compound such as an aluminum compound or tin compound. In some cases, a molecular weight adjuster comprised of an α-olefin is added. The thus obtained cyclopentene ring-opening polymer is comprised only of carbon atoms and hydrogen atoms, so is low in affinity with a filler such as carbon black or silica. For this reason, even if mixing a filler into such a cyclopentene ring-opening polymer to form a polymer composition, the effect of improvement of mechanical properties by mixing in the filler will not be sufficiently realized.
As a technique to improve the affinity of a cyclopentene ring-opening polymer with a filler, Patent Document 2 proposes the method of ring-opening polymerization of cyclopentene in the presence of a compound having a functional group and ethylenically unsaturated bond (for example, allyltrimethoxysilane etc.) using a ruthenium carbene complex as a catalyst and introducing a functional group to a cyclopentene ring-opening polymer chain end by a metathesis reaction of the cyclopentene ring-opening polymer chain end and an ethylenically unsaturated bond. The cyclopentene ring-opening polymer having a functional group at a polymer chain end obtained by this method is greatly improved in affinity with a filler compared with a cyclopentene ring-opening polymer not having a functional group.
However, if considering the rising demands for low fuel consumption performance from tires in recent years, when using a polymer composition containing a cyclopentene ring-opening polymer and filler as a composition for tire applications, improvement of the low heat buildup property of the polymer composition is desirable even for the cyclopentene ring-opening polymer obtained by the method described in Patent Document 2. For example, even if introducing an alkoxysilyl group into a cyclopentene ring-opening polymer chain end by using the method of Patent Document 2, an alkoxysilyl group being considered to have excellent performance as a functional group introduced for improving the affinity with a filler in the styrene-butadiene rubber which is currently broadly used for tire applications, there would still be room for improvement of the low heat buildup property in the polymer composition obtained by the same.